It has been known for many years that potable water could be produced from sea water or brackish water by cooling it to produce ice, separating the ice and then washing and melting the ice. When the ice forms it excludes minerals so that upon being melted water is obtained of potable quality.
Various types of freeze exchangers useful for producing ice from sea water or brackish water are disclosed in the prior art. Thus, shell and tube type falling film freeze exchangers are disclosed in Engdahl et al U.S. Pat. No. 4,286,436 and Nail U.S. Pat. No. 4,335,581. A desirable characteristic of such freeze exchangers is their ability to handle a wide quality of feeds without pretreatment.
The freeze exchanger produces an aqueous mixture comprising small ice particles and sea water or brackish water, quite often referred to as brine. A slurry of the ice and brine is generally fed from the freeze exchanger to a counterwasher in which the ice is washed free of brine. A representative counterwasher is disclosed in Nail U.S. Pat. No. 4,341,085. While counterwashers produce a clean highly pure ice, they are difficult to operate and control.
Although the mixture of ice and brine from the freeze exchanger could be fed to a conventional centrifuge instead of a counterwahser, the ice obtained from centrifugation would not be sufficiently free of brine to yield potable water when melted. Thus, the simple convenience of a centrifuge does not lead to the desired result.
From the above discussion it is believed clear that it would be highly advantageous to have available apparatus and processes for producing potable water from sea water or brackish water which make use of the inherent advantages of freeze exchangers and centrifuges.